1,984 research outputs found
Planar compact array with parasitic elements for MIMO systems
A compact planar array with parasitic elements is studied to be used in MIMO systems. Classical compact arrays suffer from high coupling which makes correlation and matching efficiency to be worse. A proper matching network improves these lacks although its bandwidth is low and may increase the antenna size. The proposed antenna makes use of parasitic elements to improve both correlation and efficiency. A specific software based on MoM has been developed to analyze radiating structures with several feed points. The array is optimized through a Genetic Algorithm to determine parasitic elements position in order to fulfill different figures of merit. The proposed design provides the required correlation and matching efficiency to have a good performance over a significant bandwidth
Massive MIMO performance evaluation based on measured propagation data
Massive MIMO, also known as very-large MIMO or large-scale antenna systems,
is a new technique that potentially can offer large network capacities in
multi-user scenarios. With a massive MIMO system, we consider the case where a
base station equipped with a large number of antenna elements simultaneously
serves multiple single-antenna users in the same time-frequency resource. So
far, investigations are mostly based on theoretical channels with independent
and identically distributed (i.i.d.) complex Gaussian coefficients, i.e.,
i.i.d. Rayleigh channels. Here, we investigate how massive MIMO performs in
channels measured in real propagation environments. Channel measurements were
performed at 2.6 GHz using a virtual uniform linear array (ULA) which has a
physically large aperture, and a practical uniform cylindrical array (UCA)
which is more compact in size, both having 128 antenna ports. Based on
measurement data, we illustrate channel behavior of massive MIMO in three
representative propagation conditions, and evaluate the corresponding
performance. The investigation shows that the measured channels, for both array
types, allow us to achieve performance close to that in i.i.d. Rayleigh
channels. It is concluded that in real propagation environments we have
characteristics that can allow for efficient use of massive MIMO, i.e., the
theoretical advantages of this new technology can also be harvested in real
channels.Comment: IEEE Transactions on Wireless Communications, 201
Interference Exploitation-based Hybrid Precoding with Robustness Against Phase Errors
Hybrid analog-digital precoding significantly reduces the hardware costs in
massive MIMO transceivers when compared to fully-digital precoding at the
expense of increased transmit power. In order to mitigate the above shortfall,
we use the concept of constructive interference-based precoding, which has been
shown to offer significant transmit power savings when compared with the
conventional interference suppression-based precoding in fully-digital
multiuser MIMO systems. Moreover, in order to circumvent the potential
quality-of-service degradation at the users due to the hardware impairments in
the transmitters, we judiciously incorporate robustness against such
vulnerabilities in the precoder design. Since the undertaken constructive
interference-based robust hybrid precoding problem is nonconvex with infinite
constraints and thus difficult to solve optimally, we decompose the problem
into two subtasks, namely, analog precoding and digital precoding. In this
paper, we propose an algorithm to compute the optimal constructive
interference-based robust digital precoders. Furthermore, we devise a scheme to
facilitate the implementation of the proposed algorithm in a low-complexity and
distributed manner. We also discuss block-level analog precoding techniques.
Simulation results demonstrate the superiority of the proposed algorithm and
its implementation scheme over the state-of-the-art methods
Mutual coupling in MIMO systems
The drive towards greater efficiency in communications systems has led to the birth of many new technologies and considerable improvements in existing systems over the last 20 years. These developments have been underpinned by increasing demands for higher data speeds, capacity and reliability by end users on a global level. Wireless communications systems have witnessed rapid transformations with this regard. Numerous enhancements in data capacities have been the hallmark of these systems. One of the principal components in achieving improved performance in wireless systems is the antenna system. Single Input Single Output (SISO) antenna topologies have traditionally been employed in wireless links. As the demand for higher data rates have persisted various limitations have arisen. Multiple Input Multiple Output (MIMO) antenna topologies have provided promise of the desired system capacity and reliability. Since MIMO systems employ two or more antenna pairs simultaneously, the effects of mutual coupling become a significant consideration in the quest to achieve high system performance. Therefore a clear understanding of mutual coupling effects with varying conditions in necessary for practical purposes. A lot of work has already been done on this subject. This thesis shall seek to substantiate some fundamental evidence on the relationship between mutual coupling effects and antenna element separation. The procedure shall involve the use of proven computer aided design software to achieve this purpose. Microstrip antennas (used interchangeably with patch antennas), widely known for their efficacy in wireless communications applications will be used for the tests. Specifically the more common linearly polarized rectangular microstrip antenna shall be utilised
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